SqlSugar子查询

1、基础教程

1.1 API目录

*****只查一列*****

//First: SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Select(s => s.Id)

//max例1: SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Max(s => s.Id)

//max例2: SqlFunc.Subqueryable<School>()..Where(s=>s.Id==st.Id).Select(s=>SqlFunc.AggregateMax(s.Id))

//min:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Min(s => s.Id)

//avg:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Avg(s => s.Id)

//count:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Count()

//sum:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Sum(s => s.num)

//去重后汇总数量

//SqlFunc.Subqueryable<School>().Where(s => z.Id == st.Id).Select(s=>SqlFunc.AggregateDistinctCount(s.Name))

//逗号分割列

//SqlFunc.Subqueryable<Order>().Where(z=>z.Id==it.Id).SelectStringJoin(z => z.Name, ",")

//完整用例：看标题8

*****返回List或者实体*****

新功能：5.1.3.36

//SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList()

//SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList(it=>new Class(){ Name=it.Name})

//更多看标题4

*****返回单个实体*****

//SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).First()

//更多看标题9

*****IN、Not in、Exists、Not Exists*****

//看标题2

1.2 where中使用

var getAll = db.Queryable<Student, School>((st, sc) => new JoinQueryInfos(JoinType.Left,st.Id==sc.Id) )

.Where(st => st.Id == SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Select(s => s.Id))

.ToList();

/*生成的MYSQL语句，如果是SqlServer就是TOP 1

SELECT `st`.`ID`,`st`.`SchoolId`,`st`.`Name`,`st`.`CreateTime`

FROM `STudent` st Left JOIN `School` sc ON ( `st`.`ID` = `sc`.`Id` )

WHERE ( `st`.`ID` =(SELECT `Id` FROM `School` WHERE ( `Id` = `st`.`ID` ) limit 0,1))

*/

1.3 在select中使用

var getAll = db.Queryable<Student, School>((st, sc) => new JoinQueryInfos(JoinType.Left,st.Id==sc.Id ))

.Select(st => new{

name = st.Name,

id = SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Select(s => s.Id)

}).ToList();

2、IN和NOT IN的操作

2.1 Exists

Exists 和 in 区别在于 Exists 扩展性更强，支持多个字段（简单的说In能实现的Exists都能实现）

//等同于IN

var getAll7 = db.Queryable<Student>()

.Where(it => SqlFunc.Subqueryable<School>().Where(s =>s.Id==it.Id).Any()).ToList();

/*生成的SQL(等于同于it.id in(select id from school)只是写法不一样

SELECT `ID`,`SchoolId`,`Name`,`CreateTime` FROM `STudent` it

WHERE (EXISTS ( SELECT * FROM `School` WHERE ( `Id` = `it`.`ID` ) ))

*/

//等同于NOT IN

var getAll8 = db.Queryable<Student>().Where(it =>

SqlFunc.Subqueryable<School>().Where(s => s.Id == it.Id).NotAny()).ToList();

/*生成的SQL

SELECT `ID`,`SchoolId`,`Name`,`CreateTime` FROM `STudent` it

WHERE (NOT EXISTS ( SELECT * FROM `School` WHERE ( `Id` = `it`.`ID` ) ))

*/

//搜索关键词：exits

2.2 In和 Not In (5.0.7.5)

在有GroupBy的情况下==自动转成 in

db.Queryable<Order>()

.Where(it=>it.Id==SqlFunc.Subqueryable<Custom>().GroupBy(z=>z.OrderId).Select(z=>z.OrderId)).ToList()

//Sql

//SELECT [Id],[Name] FROM [Order]

// WHERE [Id] in ((SELECT [OrderId] FROM [Custom] GROUP BY [OrderId]))

2.3 分页In

db.Queryable<Order>().In(it=>it.Id,db.Queryable<Order>().Skip(1).Take(100).Select(it=>it.Id)).ToList();

3、子查询中使用Sql

4、ToList()集合对象

方式1：简单方式(5.1.3.38)

直接在Select中进行ToList ,

性能: 大于循环数倍，大部分情况性能小于ThenMapper方式和导航，写法简单性能也说的过去

//请升级到 5.1.3.36+

db.Queryable<Order>()

.Select(it => new

{

CustomId = it.CustomId,

OrderId = it.Id,

OrderName = it.Name,

CustomList = SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList()

})

.ToList();

//也可以DTO

SqlFunc.Subqueryable<Custom>()

.Where(c=> c.Id == it.CustomId).

ToList(c=> new Class(){ Name=c.Name}) //转成DTO

//注意：where ToList里面 c 的别名要一致

//只查List<string>这种集合

SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList(c=>c.Name)//最新版本

//自动DTO 5.1.4.70

SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList<DTO>()

SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).ToList(it=>new DTO(){},true);//和Queryable类似

方式2：性能、功能、跨库

该功能在同类框架中性能比较好不会生成垃圾SQL ，在现有结果进行一对多操作

var treeRoot=db.Queryable<Tree>().ToList();//可以联表查询，只要返回List中有关联字段就可以

//填充子对象

//原理：数据库一次读取 In (list[0].id,list[1].id,list[2].id...) 内存分配到对应Child

//所以无论集合多少条记录 ThenMapper 只会操作一次库

db.ThenMapper(treeRoot, item =>

{

//用例1：简单填充

//参数解释：子表的ParentId和主表的Id 进行关联查询（有Select写到SetContext前面）

//可以额外加Where写SetContext前面，但是不能带有item对象,item要写SetContext里面

item.Child = db.Queryable<Tree>().SetContext(x => x.ParentId, () => item.Id, item).ToList();

//用例2：可以多属性

//item.Child=xxxx

//item.Parent=xxxx

//用例3：类型转换类转成DTO （注意：Select中的关联字段要赋值）

//item.Child = db.Queryable<Tree>()

// .Select(it=>new ViewTree(){ParentId=x.ParentId,Id=i.Id,Name=it.Name })

// .SetContext(x => x.ParentId, () => item.Id, item).ToList();

//用例4：联表填充

//item.Child=db.Queryable<Tree>()

//.LeftJoin<Tree>((i,y)=>i.ParentId==y.Id)

//.Select((i,y)=>new viewmodel(){ Parentid=i.Parentid..........})

//.SetContext(x => x.ParentId, () => item.Id, item).ToList();

});

//异步

var treeRoot=await db.Queryable<Tree>().ToListAsync();

await db.ThenMapperAsync(treeRoot, async item =>

{

//给集合赋值参数解释子表的ParentId和主表的Id 进行关联查询

item.Child =await db.Queryable<Tree>().SetContextAsync(x=>x.ParentId,()=>item.Id, item);

});

//无限层级

var treeRoot=db.Queryable<Tree>().Where(it => it.Id == 1).ToList();

//第一层

db.ThenMapper(treeRoot, item =>

{

item.Child = db.Queryable<Tree>().SetContext(x => x.ParentId, () => item.Id, item).ToList();

});

//第二层

db.ThenMapper(treeRoot.SelectMany(it=>it.Child), it =>

{

it.Child = db.Queryable<Tree>().SetContext(x => x.ParentId, () => it.Id, it).ToList();

});

//跨库

var mydb=db.GetConnection(1);

mydb.ThenMapper(root,item=>{...});

方式3：导航方式

这种已经不属于子查询了，属于另一个查询体系，详细功能：

https://www.donet5.com/Home/Doc?typeId=1188

5、子查询在Join

5.0.5.4+

var list = db.Queryable<Order>().Where(it =>

SqlFunc.Subqueryable<A>()

.LeftJoin<B>((i,y)=>i.ItemId==y.ItemId)

.InnerJoin<C>((i,y,z) => i.ItemId == z.ItemId)

.Where((i,y,z)=>i.ItemId==1)

.Any()

).ToList();

//新版本支持了Subquery.join使用 Where<T1,T2>((x,y)=> x.id==y.id)

6、子查询使用别名

如果点不出AS请升级

SqlFunc.Subqueryable<A>().AS("A01") //这样查询的就是 A01表

7、字符串拼接

5.1.1-preview14 逗号拼接

//sqlerver : FOR XML PATH

//mysql sqlite : group_concat

//oracle : listagg

//pgsql :string_agg

var list= db.Queryable<Order>()

.Select(it => new

{

//names="名字1,名字2,名字3"

names=SqlFunc.Subqueryable<custom>().

Where(z=>z.oid==it.id)

.SelectStringJoin(z => z.Name, ",")

})

.ToList();

//多字段不能有null相加 , 字段有null需要加上 z.Name??""

.SelectStringJoin(z => SqlFunc.MergeString(z.Name,"-",z.Id.ToString()), ",")

8、只查一列（top 1）

//First:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Select(s => s.Id)

//max例1:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Max(s => s.Id)

//max例2:SqlFunc.Subqueryable<School>().Where(s=>s.Id==st.Id).Select(s=>SqlFunc.AggregateMax(s.Id))

//min:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Min(s => s.Id)

//avg:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Avg(s => s.Id)

//count:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Count()

//sum:SqlFunc.Subqueryable<School>().Where(s => s.Id == st.Id).Sum(s => s.num)

//去重后汇总数量

//SqlFunc.Subqueryable<School>().Where(s => z.Id == st.Id).Select(s=>SqlFunc.AggregateDistinctCount(s.Name))

//逗号分割列

//SqlFunc.Subqueryable<Order>().Where(z=>z.Id==it.Id).SelectStringJoin(z => z.Name, ",")

//用例

Select(it=>

new{

id=it.id,

schoolname=SqlFunc.Subqueryable<School>().Where(s=>s.Id==it.ShoolId).Select(s=>s.Name)

//对应的Sql:

//schoolname=(SELECT `Name` FROM `School` `s` WHERE (`s`.`Id`=`it`.`ShoolId`)limit 0,1)

})

//如果要查整个对象：看标题9

9、子查询 First()整个对象

//需要升级5.1.4.59

var list= db.Queryable<Order>()

.Select(it => new

{

CustomId = it.CustomId,

OrderId = it.Id,

OrderName = it.Name,

CustomList = SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).First()

})

.ToList();

//可以转DTO

SqlFunc.Subqueryable<Custom>().Where(c => c.Id == it.CustomId).First(c=>new xxx(){ yy=c.id })

//如果只查一个字段：标题8